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Atomic of the Elements 1989

Cite as: Journal of Physical and Chemical Reference Data 20, 1313 (1991); https://doi.org/10.1063/1.555902 Submitted: 03 June 1991 . Published Online: 15 October 2009

J. R. De Laeter, and K. G. Heumann

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Journal of Physical and Chemical Reference Data 20, 1313 (1991); https://doi.org/10.1063/1.555902 20, 1313

© 1991 American Institute of Physics for the National Institute of Standards and Technology. a Atomic Weights of the Elements 1989 )

J. R. De Laeter

Curtin UlliversityofTechnology, Perth, Western Australia, 6001, Australia

K. G. Heumann

University ofRegensburg, Regensburg, Germany

Received June 3, 1991

The biennial review of atomic , A r (E), determinations, and other cognate data has resulted in changes for from 58.69 ± 0.01 to 58.6934 ± 0.0002 and for antimo­ ny from 121.75 ± 0.03 to 121.757 ± 0.003 due to new calibrated measurements. Because the measurement of the isotopic composition of has also been improved during the last two years, the Commission was able to reduce the uncertainty of the atomic weight of this eJement from 200.59 ± 0.03 to 200.59 ± 0.02. Due to the nearly conStant isotopic composition of in nature, where 231Pa is the predominant , the atomic weight of this element was fixed to 231.03588 ± 0.00002. The Table ofIsotopic Composi­ tions of thp Flpmpnto;;: 19R9 will hp. pllhHshed as a companion paper to that on Atomic Weights of the Elements 1989. The Table of Standard Atomic Weights Abridged to Five Significant Figures and current data on isotopic compositions of non terrestrial material are included to benefit users who are more concerned with the length of time during which a gIven table has fuB validity to the precision limit of their interest. The Table of Atomic Weights to Four Significant Figures was prepared and has been published separately.

Contents 1. Introduction ...... 1313 list of Tables 1. Standard atomic weights 1989 (alphabetical or- 2. Comments on Some Atomic Weights ...... 1314 der) ...... 1315 3. The Table of Standard Atomic Weights 1989...... 1314 2. Standard atomic weights 1989 (in order of atomic number) ...... 1317 4. Relative Atomic Masses and Half-Lives of Select- 3. Relative atomic masses and half-lives of selected ed Radionuclides ...... 1320 radionuc1ides ...... '" ...... 1319 5. Nonterrestrial Data ...... 1320 4. Examples of observed maximum isotopic varia­ tions and corresponding atomic weights due to 6. Table of Standard Atomic Weights Abridged to different processes...... 1321 Five Significant Figures...... 1322 5. Examples of isotopic composition and atomic 7. Other Projects of the Commission...... 1324 weight from different sources ...... 1322 6. Standard atomic weights abridged to five signif- 8. References...... 1325 icant figures ...... 1323

1. Introduction to the Report on the Atomic Weights of the Elements 1989 }JltSeU ttd 111:::1\::. The Commission on Atomic Weights and Isotopic The Commission has monitored the literature over the Abundances met under the chairmanship of Professor J. R. previous two years since the last report (Ref. 1) and evaluat­ Dc Lactcrfrom 10 12 August 1989, during the 35th IUPAC ed the published data on atomic weights and isotopic compo­ General Assembly in Lund, Sweden. It was decided to pub­ sitions on an element-by-element basis. The atomic weight of lish the Table ofIsotopic Compositions of the Elements 1989 an element can be determined from a knowledge of the isoto­ as determined by mass spectrometry as a companion paper pic abundances and corresponding atomic masses of the nu­ clides of that element. The latest compilation of the atomic masses with all relevant data was published in 1985 (Ref. 2) © 1991 by the U.S. Secretary of Commerce on behalf of the United States. which resulted in a number of small changes in the atomic This copyright is assigned to the American Institute of Physics and the American Chemical Society. weights that were reported in the 1985 table (Ref. 3). Al­ Reprints available from ACS; see Reprints List at back of issue. though a table with some new data was published in 1988 (Ref. 4) the Commission decided not to take them into ac­ ")Reprinted with permission of the lnternalionai Union of Pure and Ap­ count at the present because the description of these data was plied Chemistry from Pure and AppJ. Chcl1l. 63, 975 (1991). incomplete.

0047-2689/91/061313-13/$05.00 1313 J. Phys. Chem. Ref. Data, Vol. 20, No.6, 1991 1314 J. R. DE LAETER AND K. G. HEUMANN

Membership of the Commission for the 1987- 13) on the isotopic composition of . The Commis­ 1989 was as follows: sion also added footnote "g" to the atomic weight of antimo­ J. R. De Laeter (Australia, Chairman); K. G. ny because of abnormal isotopic composition found at the Heumann (FRG, Secretary); R. C. Barber (Can­ natural fission reactor site at Oklo, Gabon, West Africa ada, Associate); I. L. Barnes (USA, Associate); J. (Ref. 14). Cesario (France, Titular); T. L. Chang (China, The previous value, Ar (Sb) = 121.75, was adopted in Titular); T. B. Coplen (USA, Titular); J. W. 1962 (Ref. 15) and the uncertainty, Ur (Sb) = 0.03, was as­ Gramlich (USA, Associate); H. R. Krouse (Can­ signed in 1969 (Ref. 16). The value was based both on chem­ ada, Associate); I. A. Lebedev (USSR, Associ­ ical measurements by Willard and McAlpine (Ref. 17), ate); T. J. Murphy (USA, Associate); K. J. R. Honigschmid et al. (Ref. 18), Weatherill (Ref. 19), and Rosman (Australia, Titular); M. P. Seyfried Krishnaswami (Ref. 20) which gave an average chemical (FRG, Associate); M. Shima (Japan, Titular); K. value of Ar (Sb) = 121.751, and on the mass spectrometric Wade (UK, Associate); P. De Bievre (Belgium, measurements of White and Cameron (Ref. 9) which gave a National Representative); N. N. Greenwood calculated value of Ar (Sb) = 121.759 using current atomic (UK, National Representative); R. L. Martin mass data (Ref. 2). The assigned uncertainty included all of (Australia, National Representative); H. S. Peiser the chemical and mass spectrometric data. (USA, National Representative). The new measurement of A r (Sb) by De Laeter and Ho­ sie (Ref. 13) contains an allowance for known sources of The commision dedicates this report to Dr. I. Lynus possible systematic errors and is in excellent agreement with Barnes who died in January, 1990. Dr. Barnes was an associ­ the earlier measurement of White and Cameron (Ref. 9). ate and titular member of the Commission for 14 years, Sec­ The Commission, therefore, decided to exclude the chemical retary of the Subcommittee on the Assessment of the Isoto­ values from consideration and to base the atomic weight of pic Composition of the Elements (SAIC) from 1975 to 1983 antimony on this new measurement by mass spectrometry. and Chairman of the Commission's Subcommittee for Isoto­ There are no known variations of the isotopic composition of pic Abundance Measurements (SIAM) from 1983 to 1989. antimony except in samples from the Oklo Natural Reactor, but no systematic study of possible variations in other terre­ trial samples has been published. 2. Comments on Some Atomic Mercury: The Commission Report of 1961 proposed an Weights AT (Hg) = 200.59 based on chemical determinations (Ref. Nickel: At this meeting, the Commission has changed 21). Mass spectrometric measurements of the isotopic com­ its recommended value for the atomic weight of nickel to position of mercury agreed with the chemical measure­ Ar (Ni) 58.6934(2) based on the calibrated mass spectro­ ments, thus in 1969 the Commission assigned an uncertainty metric determination by Gramlich et al. (Ref. 5). The pre­ of Ur (Rg) = 0.03 (Ref. 16). Resulting Ar eRg) values vious value of Ar (Ni) 58.69(1), which was adopted by range only from 200.58 to 200.60. Tn 1989. the Commission the Commission in 1979, was weighted toward the chemical considered and accepted the recent gas mass spectrometric determinations of Baxter and associates (Refs. 6-8), which measurements by Zadnik, Specht, and Begemann (Ref. 22). gave an average value of Ar (Ni) 58.694. The uncertainty The Commission saw no compelling evidence to change of the 1979 value included the published mass spectrometric the proposed value for the atomic weight of mercury, values (Ref. 9-11). The excellent agreement between the Ar eRg) = 200.59, but proposed a decrease in the uncertain­ average of the chemical values and this new determination ty to Ur 0.02. The values reported for the isotopic compo­ illustrates the remarkable accuracy of the determinations of sition of mercury in Ref. 22 were also proposed by the Com­ Baxter and associates. mission as the best measurements from a single natural Gramlich et ai., in a second paper (Ref. 12), have com­ source. pared the isotopic composition of nickel in 29 minerals, salts, 3. The Table of Standard Atomic and and found no statistically significant variations. Weights 1989 Therefore, no additional allowance to the overall uncertain­ ty was necessary since the isotopic composition of terrestrial Following past practice the Table of Standard Atomic nickel is apparently invariant within the measurement un­ Weights 1989 is presented both in alphabetical order by certainty. names in English of the elements (Table 1) and in the order It should be noted that with this change the atomic of atomic number (Table 2). weight of nickel is now one of the most accurately known for The names and symbols for those elements with atomic a polynuclidic element, with a relative uncertainty of numbers 104-107 referred to in the following tables are sys~ 6 tematic and based on the atomic numbers of the elements Ur(Ni) 3X 10- , whereas the 1979 value had a relative uncertainty of 0.02%. This represents an improvement in recommended for temporary use by the IUPAC Commis­ ~ion of the N om en c:l::i tllre ofT norg~nic Chemistry (Ref. 23). accuracy uf almust twu orLlers uf magniluLle. Antimony (stibium); The Commission has changed the The names are composed of the following roots representing recommended value for the atomic weight of antimony to digits of the atomic number: Ar(Sb) = 121.757(3) from 121.75(3) based on new mass 1 un, 2 bi, 3 tri, 4 quad, 5 pent, spectrometric meausrements by De Laeter and Hosie (Ref. 6 hex, 7 sept, 8 oct, 9 enn, 10 nil.

J. Phys. Chern. Ref. Data, Vol. 20, No.6, 1991 ATOMIC WEIGHTS OF THE ELEMENTS 1989 1315

The ending "ium" is then added to these three roots, The for new precise isotopic composition measurements in order three-letter symbols are derived from the first letter of the to improve the accuracy of the atomic weights of a number of corresponding roots. elements which are still not known to a satisfactory level of The Commission again wishes to emphasize the need accuracy.

TABLE 1. Standard atomic weights 1989. [Scaled to Ar ( 12C) = 12.] The atomic weights of many elements are not invariant but depend on the origin and treatment of the material. The footnotes to this table elaborate the types of variation to be expected for individual elements~ The values of Ar (E) and uncertainties, Ur (E), in parentheses follow the last significant figure to which they are attributed, apply to elements as they exist on .

Alphabetical Order in English Atomic Atomic Name Symbol number weight Footnotes

Actinium* Ac 89 Aluminum Al 13 26.981539(5) * Am 95 Antimony (Stibium) Sb 51 121.757(3) g Ar 18 39.948(1) g As 33 74.92159(2) * At 85 Ba 56 137.327(7) * Bk 97 Be 4 9.012182(3) Bi 83 208.98037(3) B 5 10.811 (5) g m Br 35 79.904(1) Cd 48 112.411(8) g Cs 55 132.90543(5) Ca 20 40.078(4) g * Cf 98 Carbon C 6 12.011(1) Ce 58 140.115(4) g CI 17 35.4527(9) Cr 24 51.9961 (6) Co 27 58.93320( 1) Cu 29 63.546(3) * Cm 96 Dy 66 162.50(3) g * Es 99 Er 68 167.26(3) g Eu 63 151.965(9) g Ff'rminm* Fm 100 F 9 18.9984032(9) * Fr 87 Gd 64 157.25(3) g Ga 31 69.723(1 ) Ge 32 72.61(2) Au 79 196.96654(3) Hf 72 178.49(2) He 2 4.002602 (2) g Ho 67 164.93032(3) H 1 1.00794(7) g m In 49 114.82(1 ) I 53 126.90447(3) Ir 77 192.22(3) Fe 26 55.847(3) Kr 36 83.80(1) g m La 57 138.9055(2) g * Lr 103 Pb 82 207.2(1) g Li 3 6.941(2) g m Lu 71 174.967(1 ) g Mg 12 24.3050(6) Mangane~e Mil 25 5493805(1 ) MendeIevium* Md 101 Mercury Hg 80 200.59(2) Mo 42 95.94(1) g Nd 60 144.24(3) g Nl' 10 20.1797(6) g m

J. Phys. Chern. Ref. Data, Vol. 20, No.6, 1991 1316 J. R. DE LAETER AND K. G. HEUMANN

TABLE 1. Standard atomic weights J 989. I Scaled to Ar ( 12C) = 12.) The atomic weights of many elements are not invariant but depend on the origin and treatment of the material. The footnotes to this table elaborate the types of variation to be expected for individual elements. The values of Ar (E) and uncertainties, Ur (E), in parentheses follow the last significant figure to whkh they are attributed, apply to elements as tbey exist on Eartb -Continued.

Alphabetical Order in English Atomic Atomic Name Symbol number weight Footnotes

-~~--.------,,------...... -----.-- * Np 93 Nickel Ni 28 58.6934(2) Nlobium Nb 41 92.90638(2) N 7 14.00674(7) g * No 102 Os 76 190.2(1 ) g O:xygen 0 8 15.9994(3) Pd 46 106.42(1 ) g P 15 30.973762(4) Pt 78 195.08(3) '" Pu 94 * Po 84 (Kalium) K 19 39.0983( 1) Pr 59 140.90765(3) * Pm 61 Protactinium '" Pa 91 231.03588( 2) * Ra 88 * Rn 86 Re 75 186.207( 1) Rh 45 102.90550(3 ) Rb 37 85.4678(3) Ru 44 101.07(2) g Sm 62 150.36(3) g Sc 21 44.955910(9) Se 34 78.96(3) Si 14 28.0855(3) Ag 47 107.8682(2) (Natrium) Na 11 22.989768( 6) Sr 38 87.620 ) ~ultur S 16 3Z.006to) Ta 73 180.9479(1) '" Tc 43 Te 52 127.60(3) g Tb 65 158. 92534( 3) Tl 81 204.3833(2) * Th 90 232.0381 ( I ) Tm 69 168.93421 (3) Sn 50 118.710(7) Ti 22 47.88(3) (Wolfram) W 74 183.85(3) Unnilhexium* Uoh 106 Unnilpentium* Unp 105 Unnilquadium* Onq 104- Unnilseplium'" Um; 107 * V 92 238.0289( I) m V 23 50.9415(1 ) Xe 54 131.29(2) g m Yb 70 113.04(3) Y 39 88.90585(2) Zn 30 65.39(2) Zr 40 91.224(2) *Element has no stable . One Or more well-known are given in Table 3 with the appropriate relative and half-life. However, three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weigh1 is tabulated. g geological specimens are known in which the element has an isotopic composition outside the limits for normal materiaL The difference between the atomic weight of the element in such specimens and that given in the table may exceed the impHed uncertainty. m Modified isotopic compositions may be found in commercially available material because it has been subjected to an undisclosed or inadvertent isotopic s~paration. Suhstantial deviatinns in atomic weight o(thp f'lpmpnt from that given in the tahle can OCCl\r, 'l3-ange in isotopic composition of normal terrestrial material prevents a more precise AI (E) being given; the tabulated A, (E) value should be applicable to any normal material.

J. Phys. Chem, Ref. Data, Vol. 20, NO.6, 1991 ATOMIC WEIGHTS OF THE ELEMENTS 1989 1317

TABLE 2. Standard atomic weights 1989. [Scaled to Ar ( 12C) = 12.] The atomic weights of many elements are not invariant but depend on the origin and treatment of the material. The footnotes to this table elaborate the types of variation to be expected for individual elements. The values of Ar (E) and uncertainties, Ur (E), in parentheses follow the last significant figure to which they are attributed, apply to elements as they exist on Earth.

Order of Atomic Number Atomic Atomic number Name Symbol weight Footnotes

1 Hydrogen H 1.00794(7) g m 2 Helium He 4.002602(2) g 3 Lithium Li 6.941(2) g m 4 Beryllium Be 9.012182(3) 5 Boron B 10.811 (5) g m 6 Carbon C 12.011 (1) 7 Nitrogen N 14.00674(7) g 8 0 15.9994(3) g 9 Fluorine F 18.9984032(9) 10 Neon Ne 20.1797 (6) g m 11 Sodium (Natrium) Na 22.989768(6) 12 Magnesium Mg 24.3050(6) 13 Aluminum Al 26.981539(5) 14 Silicon Si 28.0855(3) 15 Phosphorus P 30.973762(4) 16 S 32.066(6) g 17 Chlorine Cl 3:5.4527 (9) m 18 Argon Ar 39.948(1 ) g 19 Potassium (Kalium) K 39.0983( 1) 20 Calcium Ca 40.078(4) g 21 Scandium Sc 44.955910(9) 22 Titanium Ti 47.88(3) 23 Vanadium V 50.9415(1 ) 24 Chromium Cr 51.9961 (6) 25 Mn 54.93805( 1) 26 Iron J:'e 55.M7(3) 27 Cobalt Co 58.93320( 1) 28 Nickel Ni 58.6934(2) 29 Copper Cu 63.546(3) 30 Zinc Zn 65.39(2) 31 Gallium Ga 69.723 ( 1) 32 Germanium Ge 72.61(2) 33 Arsenic As 74.92159(2) 34 Selenium Se 78.96(3) 35 Bromine Br 79.904( 1) 36 Krypton Kr 83.80(1 ) g m 37 Rubidium Rb 85.4678(3) g 38 Strontium Sr 87.62(1 ) g J9 Yttrium Y 88.90585(2) 40 Zirconium Zr 91.224(2) g 41 Nb 92.90638(2) 42 Molybdenum Mo 95.94(1 ) g 43 Technetium* Tc 44 Ruthenium Ru 101.07(2) g 45 Rhodium Rh 102.90550(3) 46 Palladium Pd 106.42(1 ) g 47 Silver Ag 107.8682(2) g 48 Cadmium Cd 112.411 (8) g 49 Indium In 114.82(1 ) 50 Tin Sn 118.710(7) g 51 Antimony (Stibium) Sb 121.757(3) g 52 Tellurium Te 127.60(3 ) g 53 Iodine 126.90447(3) 54 Xenon Xe 131.29(2) g m 55 Caesium Cs l32.90543(5) 56 Barium Ba 137.327(7) 57 Lanthanum La 138.9055(2) g 58 Cerium Ce 140.115(4) g 59 Praseodymium Pr 140.90765(3) 60 Neodymium Nd 144.24(3) g 61 Promethium* Pm 62 Samarium Sm 150.36(3) g 63 Europium Eu 151.965(9) g 64 Gadolinium Gd 157.25(3) g 65 Tf'rhillm Th 1"i&c),)"i':l40) 66 Dysprosium Dy 162.50(3 ) g

J. Phys. Chern. Ref. Data, Vol. 20, No.6, 1991 1318 J. R. DE LAETER AND K. G. HEUMANN

TABLE 2. Standard atomic weights 1989. [Scaled to A f ( 12C) = 12.] The atomic weights of many elements are not invariant but depend on the origin and treatment of the material. The footnotes to this table elaborate the types of variation to be expected for individual elements. The values of Ar (E) and uncertainties, Ur (E), in parentheses follow the last significant figure to which they are attributed, apply to elements as they exist on Earth -Continued.

Order of Atomic Number Atomic Atomic number Name Symbol weight Footnotes

67 Holmium Ho 164.93032(3) 68 Erbium Er 167.26(3) g 69 Thulium Tm 168.93421 (3) 70 Ytterbium Yb 173.04(3) g 71 Lutetium Lu 174.967(1) g 72 Hafnium Hf 178.49(2) 73 Tantalum Ta 180.9479(1) 74 Tungsten (Wolfram) W 183.85(3) 7S Rhenium Re 186.207(1) 76 Osmium Os 190.2(1) g 77 Iridium Ir 192.22(3) 78 Platinum Pt 195.08(3) 79 Gold Au 196.96654(3) 80 Mercury Hg 200.59(2) 81 Thallium TI 204.3833(2) 82 Lead Pb 207.2(1) g 83 Bismuth Bi 208.98037(3) 84 Polonium* Po 85 Astatine* At 86 Radon * Rn 87 Francium * Fr 88 Radium* Ra 89 * Ac 90 Thorium* Th 232.0381 ( 1 ) g 91 Protactinium * Pa 231.03588(2) 92 Uranium* U 238.0289( 1) g m 93 Neptunium * Np 94 Plutonium * Pu 95 Americium * Am 96 Curium* Cm 97 Berkelium* Bk 98 Californium * Cf 99 Einsteinium* Es 100 * Fm 101 * Md 102 Nobelium* No 103 Lawrencium* Lr 104 Unnilquadium * Unq 105 Unnilpentium* Unp 106 Unnilhexium* Unh 107 Unnilseptium * Uns *Element has no stable nuclides. One or more well-known isotopes are given in Table 3 with the appropriate and half-life. However, three :such clement:! (Th, PI1, auu U) Uu l!I1VC 11 dIl1111l:tt:li:;til: tCllc:;lli"d i:SUlupil: l:ulllpu:siliull, I111U fUl llll:::S1:: /111 /1lumil: wl::ighl i:s l/1Uul/1tl::ll. g Qeological specimens are known in which the element has an isotopic composition outside the limits for normal material. The difference between the atomic weight of the element in such specimens and that given in the table may exceed the implied uncertainty. m Modified isotopic compositions may be found in commercially available material because it has been subjected to an undisclosed or inadvertent isotopic separation. Substantial deviations in atomic weight of the element from that given in the table can occur. r gange in isotopic composition of normal terrestrial material prevents a more precise Ar (E) being given; the tabulated Ar (E) value should be applicable to any normal material.

J. Phys. Chern. Ref. Data, Vol. 20, No.6, 1991 ATOMIC WEIGHTS OF THE ELEMENTS 1989 1319

TABLE 3. Relative atomic masses and half-lives of selected radionuclides.

Atomic number Name Symbol Relative atomic mass Half-life Unit*

43 Technetium Tc 97 96.9064 2.6X 106 a 98 97.9072 4.2X 106 a 99 98.9063 2.1 X lO-~ a 61 Promethium Pm 145 144.9127 18 a 147 146.9151 2.62 a 84 Polonium Po 209 208.9824 102 a 210 209.9828 138 d 85 Astatine At 210 209.9871 8 h 211 210.9875 7.2 h 86 Radon Rn 211 210.9906 15 h 220 220.0114 56 s 222 222.0176 3.82 d 87 Francium Fr 223 223.0197 22 m 88 Radium Ra 223 223.0185 11 d 224 224.0202 3.7 d 226 226.0254 1.6X103 a 228 228.0311 " R a 89 Actinium Ac 227 227.0278 21.8 a 90 Thorium Th 230 230.0331 7.54X 104 a 232 232.0381 1.40 X 1010 a Ql Protactinium Pa 231 231.0359 3.25X 104 a 92 Uranium U 233 233.0396 1.59X 10" a 234 234.0409 2.46 X lOS a 235 235.0439 7.04x 108 a 236 236.0456 2.34X 107 a 238 238.0508 -1.-17xl09 93 Neptunium Np 237 237.0482 2.14X 106 a 239 239.0529 2.35 d 94 Plutonium Pu 238 238.0496 87.7 a 239 239.0522 2.41 X 104 a 240 240.0538 6.56X 103 a 241 241.0568 14.4 a 242 242.0587 3.75X 105 a 244 244.0642 8.0X 107 a 95 Americium Am 241 241.0568 433 a 243 243.0614 7.37X 103 a 96 Curium Cm 243 243.0614 29.1 a 244 244.0627 18.1 a 245 245.0655 8.5X 103 a 246 246.0672 4.8X 103 a 247 247.0703 1.6X 107 a 248 248.0723 3.5X 105 a 97 Berkelium Bk 247 247.0703 1.4 X 103 a 249 249.0750 3.2X 102 d 98 Californium Cf 249 249.0748 3.5 X 102 a 250 250.0764 13.1 a 251 251.0796 9.0X 102 a 252 252.0816 2.64 99 Einsteinium Es 252 252.083 1.3 a 100 Fermium Fm 257 257.0951 101 d 101 Mendelevium Md 256 256.094 76 m 258 258.10 52 d 102 Nobelium No 259 259.1009 58 m 103 Lawrencium Lr 262 262.11 216 m 104 Unnilquadium Unq 261 261.11 65 105 Unnilpentium Unp 262 262.114 34 106 Unnilhexium Unh 263 263.118 0.8 107 Unnilseptium Uns 262 262.12 0.10

*a = years; d = days; h = hours; m = minutes; s = seconds.

J. Phys. Chern. Ref. Data, Vol. 20, No.6, 1991 J. I( DI U\[TLf\ I\ND K. G. HEUMANN

.\ \\<.\;,I'\i,.I\\O\1l1C M""""" ,lila Hall-Lives ot (A~l) Fractionation by volatilization and condensation. Screelcd Radio(lucfides (A~2) Fractionation by chemical processes: This grDuping includes some special cases, such as the production of \ II" '~''')ll>,,;-;n,-,n OJ) At(..~ic V.lMsht« Elnd 18.otopic V1 gaUl\.; Uli:)..t.t';;'l. Ab\l\\Uunt:es has, for many years, pllblished a Table of Rela­ (B) Nuclear reactions tive Atomic Masses. and Half-Lives of Selected Radio­ (B-1) Nudeosynthesis: The mechanism of formation of nuclides for elements withQut a stable l'lUcIide. Since the these nucleosynthetk materials is open to question. <;:om~ssion bas flD prime responsibility for the dissemina­ Tabulated here are samples identified by tbe authors tion ot such vaJues, it has not attempted etthe.r to reca.rtl tht as products of Dllcleosynthesis. b.est preciSl?n possible or make its tabulation comp-renen­ (B-2) Spallation reactions: , produced by Sl~~. Ther~ 15 n? general ag(~ment on which of the isotopes galactic and solar cosmic ray bombardment prior to at the radtoacttve elements 1S, or is likely to be judged, "im­ the fall of the meteorite. ~l'tzU1t" . an~ vuriou~ criteria such as "lollges:t haJf.lift"," \. B~:)) Low~t!\\eIgy lht:,l m.d m:.uttQU I..oll.ptu.cc n;ll:ction3: 130m productlOn In quanhty," "used commercial1y," etc" will be bardment of the lunar surface or the interior of rne~ apposite for different situations. The relative atomic masses teorites by thermal neutrons o.rigin.atlng from cosmic a~e derived from t~e atomic masses (il\ u) recommended by rays. \\ap;tra and Audl (Kef. 2), Th. ha1f·1i,,,,, lit\ed are those prov'ded by Holden (Refs. 24-26). The data IS listed m la­ [f:) Radioactivedecay.products ble], (C- I) Products from extinct nuclides: When the solar sys­ tem .had efolved to the point where the meteorites had become closed isotopic systems some 4.6x 109 years 5. Nonterrestria\ Data ago, some radioactive nuclides, now extinct in the. so­ A rapidly expanding body of knowledge is forming on lar system. were still presem. Decay prmluct~ of Imd, the isotopic abundances of elements from nonterrestria.l nuclides are responsjble for the anomalous isotopic sources. Information about nonterrestrial isotopic abun­ composi.tion of certain dements. dances can be obtained from mass spectrometric studies of (C-2) Enrichments in the decay products of radioactive nu­ did7s- whlr.h :.:lifO ~()mmon1y used for £,:oochronologv. meteorltkt )unar and interplanetary dust materIals, trom ( C-3) Enrichments 8S 8 result of double Ii decayofeadioac­ space probes uS1ng mass and far~infrared to ultraviolet spec­ tra, from ground-based astronomical photoelectric and ra­ live nuclides with long half-lives. dio observations, and from cosmk ray analyses. (C-4) Enrichments as the result of the decay of fission prod­ ucts. \\. h.b.~ "bcc..n c!lt~b\bbcd tht1t many c\em~ntB 'nave.\'l djj~ (C~ 5) Fretere.ntlat lo'3.s of hydrogen and orhtr Ugh l ga~c.., ie!ent isotopic compos.ition in nonterrestrial materials when from the gravitat;Qnal field of the object For exam­ compared with normal terrestrial materiaJs, These effects ple, the heHum and argon in the Earth's atmosphere h~ve been demDnstrated by recent pr~ite mass -spt!ctrome­ ~re presently composed of very little of the original tne measurements of meteorite, lunar materiais., aud inter· planetary dust. Excellent reviews describing isotO'pic anom­ .bel1l.lm ann argnn gft .. hIlt instead :.1recomposed of the OLJtgossed beljum a.nd argon decay products from the alies in nonterrestrial materials are given by Anders. (Ref. heavy, naturally radioactive dements and from 4°K 27), Begemann (Ref. 28), Clayton (Ref 29), Clayton et al. respectively. ' (Ref. 30), Esat (Ref 31), Geiss and Bochsler (Ref. 32), S()urces Kerridge and Matthews (Ref. 33), Pillinger (Ref. 34), (a) fnrerplanetafY dust (cosmic dust) Reynolds (Ref. 35), Takaoka (Ref 36), Wasserburg (Ref. IsQ\.opic. IattOh of H, H'C, C, 0, Nt, Mg, and 5i in so~ 37), Wasserburg e/ al. (Ref. 38), and Wiedenbeck (Ref called interplanetary dUst collected in the strgtosphere, 39). Fowler (Ref. 40) also touched on this problem in his near the polar region or from deep-sea sediments have Nobel1ecture in Stockholm, Sweden. Those interes.ted in a been determined. more comprehensive review should refer toSbjma (Refs. 41 (b) Solar particles and 42) and Shima and Ebihara (Rei. 43). (lr-l) : LW1af samples and gas rich chondrites It is important to realize that, although mo,;t 01 the. St­ have shown evidence of isotopic modification because ported. isotopic anomahes are smaH, SDme variations are of ancient and recent soJar wind. quite large. For this r~ason, scientists deating with nonter­ (b-2) Solar flare During the solar <'ent of 23 September restriai samples shQuld e.xercise caution when the isotOplC t 978, a satellite~born "heavy isotope spectrometer composition or the atomic weight of a non terrestrial sample telescope" (HlST) successfully measured isotopic ra~ is required. tios of several dements found in the energetic particle The data have been classified according to the major ftu.xe'S emitted by the sun. natural alteration or production processes, or tbe sources of (c) Cosmic rayS' materials as described in the following outline. Data lncluded in this category are the }~s\llts. of cos.mlc­ Process ray measurements in the near~earth environment by bat~ (A) Massfractionotion loon and satellite experiments. Mass d~vendent fractionation can occur both before (c-ll Relatively low energy cosmic rays (-lO--lOOOMeV I and alter the formation of the . u)·. Th~recent development of high resolution detec-

J. Phys. Chem. Ref. Data, \lot 20, No, 6, 1991 ATOMIC WEIGHTS OF THE ELEMENTS 1989 1321

tors make it possible to measure the relative isotopic materials systematically, some examples of isotopic varia­ abundance of several elements. tions have been given in past reports. In order to provide a (c-2) High-energy cosmic rays (> 6 GeV /u): Despite ex­ more comprehensive view of current research on the isotopic perimental difficulties, 3He/4He ratios have now been variations found in non terrestrial materials, we have chosen determined. in this report to present some of these data in Tables 4 and 5. (d) Planets and satellites Table 4lists experimental results for a selection of the Isotopic ratios of some elements in planets and one of largest reported variations. This information has been classi­ the satellites of Saturn (namely Titan) were determined fied in terms of the major process involved in the modifica­ by spacecraft-born mass and infrared spectrometers and tion of the isotopic composition of the element concerned. gruuml-lmscd iufrared spectrometry. Thus, for example, the table lists, as one of the items, the ( e) Cool stars largest deviation of isotopic composition reported for the Isotopic ratios of C and 0 in cool giant and supergiant caused by a mass fractionation process, stars and Mg in -poor subgiant stars have been ob­ (A-I). Only data of enrichment or depletion of specific iso­ tained from their infrared spectra taken with large topes produced predominantly by one of the major altera­ ground-based telescopes. tion processes are listed. Data listed in Table 4 are limited to (f) Interstellar clouds measured values reported in publications and in no instance !sulupt::s uf H, Ht:, C, N, and 0 have been detected by represent interpolations or extrapolations. large ground-based photoelectric and radio-telescopes, Entries given as "8" or "u" (per atomic mass unit) are and by satellite-born ultraviolet and far-infrared spec­ all in per mil (per 1000). The "8" values are expressed by trometry. respective mass numbers, for example, the meaning of (g) Comet Halley 8( 15,14) is as follows: 18 16 D/H and 0/ 0 ratios in comet Halley were measured (15N/14N) ) by the Giotto spacecraft-born mass spectrometer on 14 8(15,14)=15( 14 n -1 XIOOO Mcuch 198G. ( NI N), Although the Commission does not attempt to review (n: nonterrestrial samples, : terrestrial standard). Where an the literature on the isotopic composition of nonterrestrial isotopic ratio or atomic weight is given, the terrestrial value

TABLE 4. Examples of observed maximum isotopic variations and corresponding atomic weights due to different processes.

Isotopic ratio Atomic Element maximum variation weight Materials Process Reference

(15,14); + 190 14.0074 C2-chondrite (A-2) 44 (14.0067) Renazzo

12.5/u InclUSIOn Cl~2 from (A-I) 45 C3-chondrite Allende 3 4°Ar/3°Ar = 1.2x 10- 36.29 1850 °C release from (C-5) 46 (295.5) (39.95) carbon-rich residue of ureilite Dyalpur 39 /40 /41 42.02/18.90/39.08 39.934 Iron meteorite (B-2) 47 (93.25/0.012/6.73 ) (39.098) Aroos

22Ti (50,48); + 104.3 Hibonite, MY-H4 (B-l) 48 from C2-chondrite Murray H4 H2Krj Kr - 0.355 1000 °C release from (C 3) -19 (0.203) FeS in iron meteorite Cape York 107Agl09Ag = 2.94 107.41 Iron meteorite Hoba (C-l) 50 ( 1.08) ( 107.87) #4213 13°Xe/IJ1Xe = 0.617 600 °C release from (C-4) 51 (0.331) < 2.89 g/cm3 density fraction of C3-chron­ drite Allende (150,154); + 7.83 LUllaI IUl;k, 10017,32 (B-3) 52

204 /206 /207 /208 1.00/301.2/190.8/1524 207.6 Whitlockite from (C-2) 53 (1.00/17.2/15.8/37.4 ) (207.2) augite Angra dos Reis

J. Phys. Chern. Ref. Data, Vol. 20, No.6, 1991 1322 J. R. DE LAETER AND K. G. HEUMANN

TABLE 5. Examples of isotopic composition and atomic weight from different sources.

Isotopic Atomic Element Source ratio weight Method Reference

~------.- ,H 2H/IH (a) Interplanetary 5.3X 10-4 1.0084 Mosquito-E*, Lea-a* collected 54 particle 0.9X 10-4 1.0079 at > 18 000 m by aircraft and measured by modified SIMS

(b-1) Solar wind 1.68 X 10-5 1.0078 500-550 °C release from lunar 55 soil 10084 (d) Venus 0.022 1.029 Pioneer Venus orbiter IMS 56 (f) Local clouds 2.0X 10-5 1.0078 Ly a by Copernicus and IUE 57 TIbK (f) Toward HR 1099 ;;;.0.09 X 10-5 1.0078 LyabyIUE 57 (g) Comet 0.6X 10-4 1.0079 Giotto spacecraft-born MS 58 Halley ~4.8X 10-4 -1.0083 Earth 1.50X 10-4 1.00794

2He 3He/4 He (b-l) Solar wind 4.8X 10-4 4.0021 ISEE-3-born IMS 59 (b-2) Solar flare 0.0026 4.0000 ISEE-3-born HIST 60 (c-l) 48-77 MeV /u 0.066 3.94 ISEE-3-born HIST 61 (c-2) > 6 GeV lu <0.17 > 3.86 Balloon-born detector 62 Earth 1.38X 10-6 4.00260

6 C 12C/13C (b-l) Solar wind 86.62 12.011 1200 °C release from lunar 63 breccia 10059 (b-2) Solar flare 105 12.009 ISEE-3-born HIST 60 (c-l) 77-194 MeV lu 14.3 12.066 ISEE-3-born c.R. detector 64 (d) Jupiter 160 12.006 Voyager IRIS 65 (e) M giants 7-20 12.13-12.05 Infrared spectra by ground- 66 based telescope (f) Local clouds 43 12.02 At 423.2 and 395.7 nm spectra 67 100-200 pc by ground-based telescope from sun Earth 89.91 12.011

----~- *Names of interplanetary particles. IRIS: Infrared Interferometer Spectrometer. SIMS: Secondary Ion Mass Spectrometer. IUE: International Ultraviolet Explorer satellite. IMS: Ion Mass Spectrometer. HIST: Caltech Heavy Isotope Spectrometer Telescope.

is listed in parentheses for comparison, suitably truncated recommended. The Commission will introduce every such where necessary to an appropriate number of significant fig­ needed change in its biennial revisions of the Standard ures. Atomic Weights even if most common sources of the ele­ Table 5 lists examples of the isotopic compositions and ment in question arc unaffected. atomic weights of elements from different sources. Thus, the details in the Table of Standard Atomic Weights in many respects exceed the needs and interests of 6. Table of Standard Atomic Weights most users who are more concerned with the length of time during which a given table has full validity to the precision Abridged to Five Significant Figures limit of their interests. The Commission in 1987 therefore The Commission on Atomic Weights and Isotopic decided to prepare for publication a revised and updated Abundances reaffirms its basic function which is to dissemi­ version of the 1981 Table of Atomic Weights to Five Signifi­ nate the most accurate information on atomic weights with cant Figures (Ref. 68), or fewer where uncertainties do not their associated uncertainties as they are currently published warrant even five-figure accuracy (this currently applies to in the literature and carefully evaluated by the Commission. ten elements) . It does not try to judge whether the sixth, seventh or any Since the publication of the earlier, first version of the significant figure could ever be of interest to any user of the abridged table, IUPAC has approved the use of the designa­ Table of Standard Atomic Weights. If published work tion "standard" to its atomic weights. This adjective is now to a standard atomic weight (or its uncertainty) that is con­ also illl;Ol porate:d in the: title of the: revised abridged table. sidered by the Commission to be reliable and different from When an atomic weight is known to more than five signifi­ the currently tabulated value, or if convincing evidence be­ cant figures, it is abridged in this table to the five-figure value comes available in the literature for the elimination or intro­ closest to the unabridged best value given in this report. duction of an annotation, a change in the full table will be When the sixth digit ofthe unabridged value is five exactly, it

J. Phys. Chern. Ref. Data, Vol. 20, No.6, 1991 ATOMIC WEIGHTS OF THE ELEMENTS 1989 1323

TABLE 6. Standard atomic weights abridged to five significant figures. [Scaled to Ar (12C) = 12.] Atomic weights are quoted here to five significant figures unless the dependable accuracy is more limited either by the combined uncertainties of the best published atomic-weight determinations, or by the variability of isotopic composition in normal terrestrial occurrences (the latter applies to elements annotated r). The last significant figure of each tabulated value is considered reliable to ± 1 except when a larger single-digit uncertainty is inserted in parentheses following the atomic weight. Neither the highest nor the lowest actual atomic weight of any normal sample is thought likely to differ from the tabulated value by more than the assigned uncertainty. However, the tabulated values do not apply either to samples of highly exceptional isotopic composition arising from most unusual geological occurrences (for elements annotated g) or to those whose isotopic composition has been artificially altered. Such might even be found in commerce without disclosure of that modification (for elements annotated m). Elements annotated by an asterisk (*) have no stable isotope and are generally represented in this table by just one of the element's commonly known radioisotopes, with a corresponding relative atomic mass in the atomic-weight column. However, three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated. For moredetailed information users should refer to the full IUPAC Table of Standard Atomic Weights, as is found in the biennial reports of the Commission on Atomic Weights and Isotopic Abundances. They are publlshed In l'ure and Applied Chemistry.

Atomic Atomic number Name Symbol weight Annotation

1 Hydrogen H 1.0079 g m 2 Helium He 4.0026 3 Lithium Li 6.941 (2) g m r 4 Beryllium Be 9.0122 5 Boron B 10.811(5) g m r 6 Carbon C 12.011 r 7 Nitrogen N 14.007 8 Oxygen 0 15.999 9 Fluorine F 18.998 10 Neon Ne 20.180 m 11 Sodium (Natrium) Na 22.990 12 Magnesium Mg 24.305 13 Aluminum Al 26.982 14 Silicon Si 28.086 15 Phosphorus P 30.974 16 Sulfur S 32.066(6) g 17 Chlorine CI 35.453 m 18 Argon Ar 39.948 g 19 Potassium (Kalium) K 39.098 20 Calcium Ca 40.078(4) g 21 Scandium Sc 44.956 22 Titanium Ti 47.88(3) 23 Vanadium V 50.942 24 Chromium Cr 51.996 25 Manganese Mn 54.938 26 Iron Fe 55.847(3) 27 Cobalt Co 58.933 28 Nickel Ni 58.693 29 Copper Cu 63.546(3) 30 Zinc Zn 65.39(2) 31 Gallium Ga 69.723 32 Germanium Ge 72.61(2) 33 Arsenic As 74.922 34 Selenium Se 78.96(3) 35 Bromine Br 79.904 36 Krypton Kr 83.80 g m 37 Rubidium Rb 85.468 38 Strontium Sr 87.62 g 39 Yttrium Y 88.906 40 Zirconium Zr 91.224(2) g 41 Niobium Nb 92.906 42 Molybdenum Mo 95.94 g 43 Technetium* 99Tc 98.906 44 Ruthenium Ru 101.070.) 45 Rhodium Rh 102.91 46 Palladium Pd 106.42 g 47 Silver Ag 107.87 48 Cadmium Cd 112.41 49 Indium In 114.82 50 Tin Sn 118.71 51 Antimony (Stibium) Sb 121.76 g 52 Tellurium Te 127.60(3) g 53 Iodine 126.90 54 Xenon Xe 131.29(2) g m 55 Caesium Cs 132.91 56 Barium Ba 137.33 57 Lanthanum La 138.91 58 Cerium Ce 140.12 g

J. Phys. Chern. Ref. Data, Vol. 20, No.6, 1991 1:1)11 .L H. DE LAElERAND K. G. HEUMANN

'1 ,\lIl.I: h, (Ctllllillllnl)

---_._------"------_. __ .- _ .. _- - ._------Atomic Atomic number Name Symbol weight Annotation

59 Praseodymium Pr 140.91 60 Neodymium Nd 144.24(3) g 61 Promethium * 147Pm 146.92 62 Samarium Sm 150.36(3) g 63 Europium Eu 151.96 g 64 Gadolinium Gd 157.25(3) g 65 Terbium Tb 158.93 66 Dysprosium Dy 162.50(3) g 67 Holmium Ho 164.93 68 Erbium Er 167.26(3) g 69 Thulium Tm 168.93 70 Ytterbium Yb 173.04(3) g 71 Lutetium Lu 174.97 g 72 Hafnium Hf 178.49(2) 73 Tantalum Ta 180.95 74 Tungsten (Wolfram) W llB.~5(J) 75 Rhenium Re 186.21 76 Osmium Os 190.2 g 77 Iridium Ir 192.22(3) n Platinum Pt 195.08(3) 79 Gold Au 196.97 80 Mercury Hg 200.59(2) 81 Thallium TI 204.38 82 Lead Pb 207.2 g 83 Bismuth Bi 208.98 84 Polonium* 21OpO 209.98 85 Astatine* 210At 209.99 86 Radon * 222Rn 222.02 87 Francium * 223Fr 223.02 88 Radium* 226Ra 226.03 89 Actinium* 227Ac 227.03 90 Thorium* Th 232.04 g 91 Protactinium * Pa 231.04 92 Uranium * U 238.03 g m 93 Neptunium* 237Np 237.05 94 Plutonium * 239pU 239.05 95 Americium* 241Am 241.06 96 Curium* 244Cm 244.06 97 Berkelium* 249Bk 249.08 98 Californium * 252Cf 252.08 99 Einsteinium * 252Es 252.08 100 Fermium* 257Fm 257.10 101 Mendelevium* 258Md 258.10 102 Nobelium* 259No 259.10 103 Lawrencium * 262Lr 262.11

is rounded up or down to make the fifth digit in this abridged quire revision for about ten years, whereas the unabridged table even. The single-digit uncertainty in the tabulated table is revised every two years. atomic weight is hdd to be SYIIlIIlt;tril.;, lhiil is, it is iippliciibk This Table may be freely reprinted provided it includes with either a positive or a negative sign. the annotations and the rubric at the head of the Table, and The abridged table is given here as Table 6 with the provided the IUPAC source is acknowledged. reasonable hope that the quoted values will not need to be changed for several years at least-a desirable attribute for textbooks and numerical tables derived from atomic-weight 7. Other Projects of the Commission data. However, it should be remembered that the best atom­ The Four Figure Tableo!Atomic Weights was published ic-weight values of 30 elements are still uncertain by more in Chemistry Internationa169 and in International N ewslet­ than one unit in the fifth significant figure. Relevant warn­ ters on Chemical Education.70 ings of anomalous geological occurrences, isotopically al­ The Working Party on Natural Isotopic Fractionation tered materials, and variability of radioactive elements are presented a preliminary report. It was agreed that a final included in the abridged table. It is unlikely that it will re- report about the proposed work (for the elements H, Li, B,

J. Phys. Chern. Ref. Data, Vol. 20, No.6, 1991 ATOMIC WEIGHTS OF THE ELEMENTS 1989 1325

C, N, 0, Ne, Mg, Si, S, CI, K, Cu, Se, Pd, Te, and U) should 30R. N. Clayton, R. W. Hinton, and A. M. Davis, Philos. Trans. R. Soc. be presented at the next meeting of the Commission in 1991. London, Ser. A 325, 483-501 (1988). 31T. M. Esat, Geochim. Cosmochim. Acta, 52, 1409-1424 (1988). It is intended that this information will be published. 321. Geiss and P. Bochsler, Geochim. Cosmochim. Acta 46, 529-548 The Commission established a new Working Party on (1982). Statistical Evaluation of Isotopic Abundances. The aim of 33J. F. Kerridge and M. S. Matthews (editors), Meteorites and the Early this Working Party consists in presenting a classification of Solar System (Univ. Arizona Press, Tempe, 1988). 34C. T. Pill inger, Geochim. Cosmochim. Acta 48, 2739-2766 (1984). isotopic measurements for the next meeting of the Commis­ 35J. H. Reynolds, Proc. R. A. Welch Foundation Conf. Chern. Res. XXI. sion. 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